1. Field of the Invention
The present invention relates to piezoelectric vibration devices and to piezoelectric resonance components for use in piezoelectric resonators, piezoelectric filters, and other similar devices. More specifically, the present invention relates to a piezoelectric vibration device and a piezoelectric resonance component each having a beveled surface located near each end of a piezoelectric element.
2. Description of the Related Art
Energy-trapping piezoelectric devices have been widely used in resonators, band-pass filters, and other similar devices. An example of a piezoelectric device of this sort is disclosed in Japanese Unexamined Patent Publication No. 56-165413. FIG. 7 of the present application shows a perspective view of a piezoelectric device described in the related art. A piezoelectric device 51 includes a piezoelectric substrate 52. The piezoelectric substrate 52 is polarized along a direction indicated by an arrow P in FIG. 7, that is, in a direction parallel to the main surface of the substrate 52. At the centers of the top surface and the bottom surface of the piezoelectric substrate 52, vibration electrodes 53 and 54 are provided so as to oppose each other with the piezoelectric substrate 52 disposed therebetween. The vibration electrode 53 is electrically connected to a terminal electrode 55 located at one end of the piezoelectric substrate 52. On the bottom surface of the piezoelectric substrate 52, the vibrating electrode 54 is connected to a terminal electrode 56 located on the other end of the piezoelectric substrate 52.
In the piezoelectric device 51, at least one of four ridges at longitudinal ends of the piezoelectric substrate 52 is cut along a width direction of the piezoelectric substrate 52. In other words, beveled surfaces 52a and 52b are formed at opposite ends of the substrate 52.
In the piezoelectric device 51, by properly setting dimensions of the beveled surfaces 52a and 52b, spurious responses generated due to a longitudinal mode may be suppressed.
Also, as disclosed in Japanese Unexamined Utility Model Publication No. 1-40920, a piezoelectric resonator that generates thickness shear vibration has beveled surfaces at both ends of a piezoelectric substrate. In this device, by forming a beveled surface at end of the piezoelectric substrate, energy trap efficiency is increased and filtering characteristics are improved. This publication also describes that spurious responses due to a contour mode may be suppressed, and it is easier to make the device compact.
As described in the above-mentioned related art, in an energy-trapping piezoelectric device which generates thickness shear vibration, it is known that by forming a beveled surface on a piezoelectric substrate, spurious responses due to a longitudinal mode or a contour mode may be suppressed, and energy trap efficiency may be increased.
However, in a conventional energy-trapping piezoelectric device having a beveled surfaces, a problem occurs in that by increasing energy trap efficiency, a response of a higher-order mode vibration which results in spurious responses is greatly increased.
When a thickness shear mode energy-trapping piezoelectric device is utilized as an oscillator, suppression of harmonics generated at frequencies of odd-number multiples of a fundamental vibration is absolutely necessary. When suppression of the harmonics is insufficient, oscillations are likely to occur at frequencies of odd-number multiples, such as three times, five times, and other multiples, of a transmission frequency.
To overcome the problems described above, preferred embodiments of the present invention provide an energy-trapping piezoelectric vibration device arranged to generate a thickness shear mode and to effectively suppresses spurious responses due to a longitudinal direction mode and a contour mode and also effectively suppresses spurious responses due to higher-order modes, thus realizing improved resonance and filtering characteristics.
A preferred embodiment of the present invention provides a piezoelectric vibration device having a piezoelectric element including first and second longitudinally opposed ends, top and bottom surfaces provided between the first and second ends such that the top and bottom surfaces oppose each other, and beveled surfaces disposed at a vicinity of the first and second ends such that the thickness of the piezoelectric element gradually decreases towards the first and second ends, respectively, and first and second vibration electrodes disposed on the top surface and the bottom surface of the piezoelectric element, respectively, the first and second vibration electrodes located substantially at a middle portion of the piezoelectric element so as to oppose each other with the piezoelectric element disposed therebetween to define opposing portions which constitute a vibrator, wherein a roughness of the beveled surfaces is greater than a roughness of the surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes.
Preferably, Ra1xe2x88x92Ra2 greater than 0.3 xcexcm is satisfied where Ra1 is the mean roughness of the center line according to Japanese Industrial Standard B0601 of the beveled surface, and Ra2 is the mean roughness of the center line of the surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes.
In the present invention, the beveled surfaces may be provided on the top surface only, or the bottom surface only, or on the top and bottom surfaces.
In another preferred embodiment of the present invention, there is provided a piezoelectric resonance component including a case substrate, a piezoelectric vibration device mounted on the case substrate, and a case member mounted on the case substrate so as to enclose the piezoelectric vibration device, wherein the piezoelectric vibration device includes a piezoelectric element including first and second longitudinally opposed ends, top and bottom surfaces provided between the first and second ends such that the top and bottom surfaces oppose each other, and beveled surfaces disposed at a vicinity of the first and second ends such that the thickness of the piezoelectric element gradually decreases towards the first and second ends, respectively; and first and second vibration electrodes disposed on the top surface and the bottom surface of the piezoelectric element, respectively, the first and second vibration electrodes located substantially at a middle portion of the piezoelectric element so as to oppose each other with the piezoelectric element disposed therebetween to define opposing portions which constitute a vibrator, and wherein a roughness of the beveled surfaces is greater than a roughness of a surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes.
Preferably, the above described piezoelectric resonance component further includes a capacitor device mounted on the case substrate, wherein the piezoelectric vibration device is secured on the capacitor device and mounted on the case substrate via the capacitor device, and a built-in load capacitance type oscillator is configured by the above arrangement. Note that when a capacitor device is mounted on the case substrate and when the piezoelectric vibration device is secured on the capacitor device, a piezoelectric resonance component that oscillates positively at a desired frequency and is free from abnormal oscillations or other defects is obtained.
In preferred embodiments of the present invention, since a beveled surface is provided on a piezoelectric element having an energy-trapping piezoelectric vibrator, spurious responses due to a longitudinal mode or a contour mode are effectively suppressed. Further, since the surface roughness of the beveled surface is greater than the surface roughness of the surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes, spurious responses due to higher-order modes are also effectively suppressed.
Consequently, a piezoelectric vibration device that has superior energy trapping, reduced influence from unwanted spurious responses, and superior resonance and filtering characteristics is provided.
Note that, when the center line mean roughness Ra1 of the beveled surfaces and the center line mean roughness Ra2 of the flat surfaces of a piezoelectric element has a relationship expressed by Ra1xe2x88x92Ra2 greater than 0.3 xcexcm, spurious responses due to higher-order modes is even more effectively suppressed.
Further, in a preferred embodiment having a pair of beveled surfaces provided in the vicinity of the ends of the top surface of a piezoelectric element and having no beveled surface provided on the bottom surface of the piezoelectric element, the piezoelectric element can have the bottom surface mounted on a case substrate, a printed circuit board or other substrate, in a very reliable and stable mounting arrangement.
When a pair of beveled surfaces are provided at the longitudinally opposed ends of the top surface and bottom surface of a piezoelectric element, the piezoelectric element can be mounted with ease on a case substrate or other type of substrate, using an automatic procedure without having to arrange the piezoelectric element to have a certain directional orientation, because the top and bottom surfaces have identical configurations.
In preferred embodiments of the present invention, the piezoelectric vibration device may be made of piezoelectric ceramic material, piezoelectric single crystal material or other suitable piezoelectric material so that various resonance characteristics and filtering characteristics can be realized with ease by controlling the composition of the piezoelectric material.
In a piezoelectric resonance component according to a preferred embodiment of the present invention, since a piezoelectric vibration device according to a preferred embodiment is mounted on a case substrate, and a casing member is fixed to the case substrate so as to surround the piezoelectric vibration device, a piezoelectric resonance component having greatly improved resonance characteristics and filtering characteristics, in which unwanted spurious responses are suppressed, and which is capable of being easily mounted on a printed circuit board or other substrate, can be provided.
Further, in a piezoelectric resonance component according to a preferred embodiment of the present invention, when a capacitor device mounted on a case substrate is provided, a piezoelectric vibration device is securely mounted on the capacitor device, and a built-in load capacitance type piezoelectric oscillator includes a piezoelectric vibration device and a capacitor device, the built-in load capacitance type piezoelectric oscillator can be configured by a single piezoelectric resonance component, and a piezoelectric vibration device according to a preferred embodiment of the present invention is provided therein. As a result, a piezoelectric resonance component which positively oscillates at a desired frequency and is free from abnormal oscillations or other problems, is provided.
Other features, elements and advantages of the present invention will be described in detail below with reference to preferred embodiments of the present invention and the attached drawings.